Focus adjusting pancharatnam berry phase liquid crystal lenses in a head-mounted display

ABSTRACT

A varifocal block includes, in optical series, a switchable half waveplate (SHWP) and a plurality of liquid crystal (LC) lenses. The SHWP outputs circularly polarized light, and a handedness of the circularly polarized light is controlled by the SHWP being in an active state or a non-active state. Each LC lens of the plurality of LC lenses has a plurality of optical states, the plurality of optical states including an additive state that adds optical power to the LC lens and a subtractive state that removes optical power from the LC lens. The plurality of optical states of each of the plurality of the LC lenses compounded in optical series provides a range of adjustment of optical power for the varifocal block.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/425,922, filed Nov. 23, 2016, which is incorporated by reference inits entirety.

BACKGROUND

The present disclosure generally relates to adaptive visual images fromelectronic displays, and specifically to varying the focal length ofoptics to enhance comfortable viewing experience in head mounteddisplays.

Virtual reality (VR) headset can be used to simulate virtualenvironments. For example, stereoscopic images can be displayed on anelectronic display inside the headset to simulate the illusion of depthand head tracking sensors can be used to estimate what portion of thevirtual environment is being viewed by the user. Such a simulation,however, can cause visual fatigue and nausea resulting from an inabilityof existing headsets to correctly render or otherwise compensate forvergence and accommodation conflicts. Augmented Reality (AR) headsetsdisplay a virtual image overlapping with the real world. To createcomfortable viewing experience, the virtual image generated by the ARheadsets needs to be displayed at the right distance for the eyeaccommodations of the real world objects at different time.

SUMMARY

A varifocal block has a range of adjustment of optical power. Thevarifocal block includes a switchable half waveplate (SHWP) and aplurality of liquid crystal (LC) lenses. The SWHP and the plurality ofLC lenses are in optical series with each other. The SHWP outputscircularly polarized light, and a handedness of the circularly polarizedlight is controlled by the SHWP being in an active state or a non-activestate. And each LC lens of the plurality of LC lenses has a plurality ofoptical states. The plurality of optical states include an additivestate that adds optical power to a LC lens and a subtractive state thatremoves optical power from the LC lens. The plurality of optical statesof each of the plurality of the LC lenses compounded in optical seriesprovides a range of adjustment of optical power for the varifocal block.

The varifocal block may be part of a head-mounted display (HMD). The HMDpresents content via an electronic display to a wearing user at a focaldistance. The varifocal block presents the content over a plurality ofimage planes that are associated with different optical powers of thevarifocal block. As noted above, the varifocal block has a range ofadjustment of optical power. Each value of optical power over the rangeof adjustment of optical power corresponds to a different image plane ofthe plurality of image planes. In some embodiments, the varifocal blockadjusts the image plane location in accordance with instructions fromthe HMD to, e.g., mitigate vergence accommodation conflict of eyes ofthe wearing user. The image plane location is adjusted by adjusting anoptical power associated with the varifocal block, and specifically byadjusting the optical powers associated with one or more of the LClenses in the plurality of LC lenses, and a state of at least one SHWP.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows the relationship between vergence and eye focal length inthe real world.

FIG. 1B shows the conflict between vergence and eye focal length in athree-dimensional display screen.

FIG. 2A is a wire diagram of a head-mounted display, in accordance withan embodiment.

FIG. 2B is a cross section of a front rigid body of the head-mounteddisplay in FIG. 2A, in accordance with an embodiment.

FIG. 3A is an example Pancharatnam Berry Phase liquid crystal lens,according to an embodiment.

FIG. 3B is an example of liquid crystal orientations in the PancharatnamBerry Phase liquid crystal lens of FIG. 3A, according to an embodiment.

FIG. 3C is a portion of liquid crystal orientations in the PancharatnamBerry Phase liquid crystal lens of FIG. 3A, according to an embodiment.

FIG. 4 is a generic design of a stacked PBP liquid crystal lensstructure that includes a plurality of active PBP liquid crystal lens,according to an embodiment.

FIG. 5A is a diagram of a stacked Pancharatnam Berry Phase liquidcrystal lens structure that includes a plurality of active PancharatnamBerry Phase liquid crystal lens, according to an embodiment.

FIG. 5B is a table showing example optical power adjustments in thepositive range of the stacked active Pancharatnam Berry Phase liquidcrystal lens structure shown in FIG. 5A, according to an embodiment.

FIG. 5C is a table showing example optical power adjustments in thenegative range of the stacked active Pancharatnam Berry Phase liquidcrystal lens structure shown in FIG. 5A, according to an embodiment.

FIG. 6A is a diagram of a stacked Pancharatnam Berry Phase liquidcrystal lens structure that includes a plurality of active PBP liquidcrystal lens and a plurality of switchable half waveplates, according toan embodiment.

FIG. 6B is a table showing example optical power adjustments in thepositive range of the stacked active Pancharatnam Berry Phase liquidcrystal lens structure shown in FIG. 6A, according to an embodiment.

FIG. 6C is a table showing example optical power adjustments in thenegative range of the stacked active Pancharatnam Berry Phase liquidcrystal lens structure shown in FIG. 6A, according to an embodiment.

FIG. 7A is a diagram of a stacked Pancharatnam Berry Phase liquidcrystal lens structure that includes a plurality of passive PancharatnamBerry Phase liquid crystal lenses and a plurality of switchable halfwaveplates, according to an embodiment.

FIG. 7B is a table showing example optical power adjustments in thepositive range of the stacked passive Pancharatnam Berry Phase liquidcrystal lens structure shown in FIG. 7A, according to an embodiment.

FIG. 7C is a table showing example optical power adjustments in thenegative range of the stacked passive Pancharatnam Berry Phase liquidcrystal lens structure shown in FIG. 7A, according to an embodiment.

FIG. 8 is multifocal system in which a HMD operates, according to anembodiment.

FIG. 9 is a process for mitigating vergence-accommodation conflict byadjusting the focal length of a HMD, according to an embodiment.

FIG. 10 shows an example process for mitigating vergence-accommodationconflict by adjusting a focal length of a multifocal block that includestwo stacked LC structures, in accordance with an embodiment.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles, or benefits touted, of the disclosure described herein.

DETAILED DESCRIPTION

Configuration Overview

A multifocal system includes a head-mounted display (HMD). The HMDincludes one or more multifocal blocks that adjust a focal distance atwhich images are presented to a user of the HMD. A multifocal blockincludes a plurality of Pancharatnam Berry Phase (PBP) liquid crystallenses in optical series. The HMD presents content via an electronicdisplay to a wearing user at a focal distance. The multifocal adjuststhe focal distance in accordance with instructions from the HMD to,e.g., mitigate vergence accommodation conflict of eyes of the wearinguser. The focal distance is adjusted by adjusting an optical powerassociated with the multifocal block, and specifically by adjusting therespective optical powers associated with one or more of the PBP liquidcrystal lenses within the multifocal. Optical series refers to relativepositioning of a plurality of optical elements such that light, for eachoptical element of the plurality of optical elements, is transmitted bythat optical element before being transmitted by another optical elementof the plurality of optical elements. Moreover, ordering of the opticalelements does not matter. For example, optical element A placed beforeoptical element B, or optical element B placed before optical element A,are both in optical series. Similar to electric circuitry design,optical series represents optical elements with their optical propertiescompounded when placed in series.

The multifocal block includes one or more stacked PBP liquid crystalstructures. Multiple PBP liquid crystal lenses and at least one halfwaveplate are coupled together in optical series to form a stacked PBPliquid crystal structure that has a tunable range of optical power. Aseach PBP liquid crystal lens provides a particular amount of opticalpower, the tunable range of optical power is determined in part by anumber of PBP liquid crystal lenses in each stacked PBP liquid crystalstructure and how much optical power a particular PBP liquid crystallens can provide. PBP liquid crystal lenses may also be active (alsoreferred to as an active element) or passive (also referred to as apassive element). An active PBP liquid crystal lens has three opticalstates. The three optical states are an additive state, a neutral state,and a subtractive state. The additive state adds optical power to thesystem (i.e., has a positive focus of ‘f’), the neutral state does notaffect the optical power of the system (and does not affect thepolarization of light passing through the active PBP liquid crystallens), and the subtractive state subtracts optical power from the system(i.e., has a negative focus of ‘−f’). The state of an active PBP liquidcrystal lens is determined by the by the handedness of polarization oflight incident on the active PBP liquid crystal lens and an appliedvoltage. An active PBP liquid crystal lens operates in a subtractivestate responsive to incident light with a right handed circularpolarization and an applied voltage of zero (or more generally belowsome minimal value), operates in an additive state responsive toincident light with a left handed circular polarization and the appliedvoltage of zero (or more generally below some minimal value), andoperates in a neutral state (regardless of polarization) responsive toan applied voltage larger than a threshold voltage which aligns liquidcrystal with positive dielectric anisotropy along with the electricfield direction. Note that if the active PBP liquid crystal lens is inthe additive or subtractive state, light output from the active PBPliquid crystal lens has a handedness opposite that of the light inputinto the active PBP liquid crystal lens. In contrast, if the active PBPliquid crystal lens is in the neutral state, light output from theactive PBP liquid crystal lens has the same handedness as the lightinput into the active PBP liquid crystal lens.

A switchable half wave plate (SHWP) is used to switch the handedness ofthe polarization of light incident on an PBP liquid crystal lens.Therefore, one gets the freedom of selecting a positive focus or anegative focus of the PBP LC lens by using the EHWP.

In contrast, a passive PBP liquid crystal lens has two optical states,specifically, an additive state and a subtractive state. And the stateof a passive PBP liquid crystal lens is determined by the handedness ofpolarization of light incident on the passive PBP liquid crystal lens. Apassive PBP liquid crystal lens operates in a subtractive stateresponsive to incident light with a right handed polarization andoperates in an additive state responsive to incident light with a lefthanded polarization. Note that the passive PBP liquid crystal lensoutputs light that has a handedness opposite that of the light inputinto the passive PBP liquid crystal lens.

Combinations of PBP liquid crystal lenses may be stacked together togenerate a multifocal block within a HMD. Some, or all, of the stackedPBP liquid crystal lenses may adjust the optical power of the multifocalblock by different amounts (e.g., a first PBP liquid crystal lens maycause a ±0.25 diopter change in optical power, and a second PBP liquidcrystal lens may cause a ±0.75 diopter change in optical power). Eachstack of the multifocal system includes at least one switchable halfwaveplate (SHWP). The multifocal block uses the SHWP to control thehandedness of polarization of light in accordance with a switchingstate. The switching state of a SHWP is either active or non-active.When active, the SHWP reverses the handedness of polarized light, andwhen non-active, the SHWP transmits polarized light without affectingthe handedness. Accordingly, using a plurality of stacked PBP lenses andat least one SHWP allows the multifocal system to generate a tunablerange of focal distances.

In some embodiments, a virtual object is presented on the electronicdisplay of the HMD that is part of the multifocal system. The lightemitted by the HMD is configured to have a particular focal distance,such that the virtual scene appears to a user at a particular focalplane. As the content to be rendered moves closer/farther from the user,the HMD correspondingly instructs the multifocal block to adjust thefocal distance to mitigate a possibility of a user experiencing aconflict with eye vergence and eye accommodation. Additionally, in someembodiments, the HMD may track a user's eyes such that the multifocalsystem is able to approximate gaze lines and determine a gaze pointincluding a vergence depth (an estimated point of intersection of thegaze lines) to determine an appropriate amount of accommodation toprovide the user. The gaze point identifies an object or plane of focusfor a particular frame of the virtual scene and the HMD adjusts thedistance of the multifocal block to keep the user's eyes in a zone ofcomfort as vergence and accommodation change.

Vergence-Accommodation Overview

Vergence-accommodation conflict is a problem in many virtual realitysystems. Vergence is the simultaneous movement or rotation of both eyesin opposite directions to obtain or maintain single binocular vision andis connected to accommodation of the eye. Under normal conditions, whenhuman eyes look at a new object at a distance different from an objectthey had been looking at, the eyes automatically change focus (bychanging their shape) to provide accommodation at the new distance orvergence depth of the new object. FIG. 1A shows an example of how thehuman eye experiences vergence and accommodation in the real world. Inthe example of FIG. 1A, the user is looking at a real object 100 (i.e.,the user's eyes are verged on the real object 100 and gaze lines fromthe user's eyes intersect at real object 100.). As the real object 100is moved closer to the user, as indicated by the arrow in FIG. 1A, eacheye 102 rotates inward (i.e., convergence) to stay verged on the realobject 100A. As the real object 100 gets closer, the eye 102 must“accommodate” for the closer distance by changing its shape to reducethe power or focal length. Thus, under normal conditions in the realworld, the vergence depth (d_(v)) equals the focal length (d_(f)).

FIG. 1B shows an example conflict between vergence and accommodationthat can occur with some three-dimensional displays. In this example, auser is looking at a virtual object 100B displayed on an electronicscreen 104; however, the user's eyes are verged on and gaze lines fromthe user's eyes intersect at virtual object 100B, which is a greaterdistance from the user's eyes than the electronic screen 104. As thevirtual object 100B is rendered on the electronic display 104 to appearcloser to the user, each eye 102 again rotates inward to stay verged onthe virtual object 100B, but the power or focal length of each eye isnot reduced; hence, the user's eyes do not accommodate as in FIG. 1A.Thus, instead of reducing power or focal length to accommodate for thecloser vergence depth, each eye 102 maintains accommodation at adistance associated with the electronic display 104. Thus, the vergencedepth (d_(v)) often does not equal the focal length (d_(f)) for thehuman eye for objects displayed on 3D electronic displays. Thisdiscrepancy between vergence depth and focal length is referred to as“vergence-accommodation conflict.” A user experiencing only vergence oraccommodation and not both will eventually experience some degree offatigue and nausea, which is undesirable for virtual reality systemcreators.

Head-Mounted Display Overview

FIG. 2A is a wire diagram of a HMD 200, in accordance with anembodiment. The HMD 200 includes a front rigid body 205 and a band 210.The front rigid body 205 includes one or more electronic displayelements of an electronic display (not shown), an IMU 215, the one ormore position sensors 220, and the locators 225. In the embodiment shownby FIG. 2A, the position sensors 220 are located within the IMU 215, andneither the IMU 215 nor the position sensors 220 are visible to theuser. The IMU 215, the position sensors 220, and the locators 225 arediscussed in detail below with regard to FIG. 7. Note in embodiments,where the HMD 200 acts as an AR or MR device portions of the HMD 200 andits internal components are at least partially transparent.

FIG. 2B is a cross section 250 of the front rigid body 205 of theembodiment of the HMD 200 shown in FIG. 2A. As shown in FIG. 2B, thefront rigid body 205 includes an electronic display 255 and a multifocalblock 260 that together provide image light to an exit pupil 263. Theexit pupil 263 is the location of the front rigid body 205 where auser's eye 265 is positioned. For purposes of illustration, FIG. 2Bshows a cross section 250 associated with a single eye 265, but anothermultifocal block 260, separate from the multifocal block 260, providesaltered image light to another eye of the user. Additionally, the HMD200 includes an eye tracking system (not shown). The eye tracking systemmay include, e.g., one or more sources that illuminate one or both eyesof the user, and one or more cameras that captures images of one or botheyes of the user.

The electronic display 255 displays images to the user. In variousembodiments, the electronic display 255 may comprise a single electronicdisplay or multiple electronic displays (e.g., a display for each eye ofa user). Examples of the electronic display 255 include: a liquidcrystal display (LCD), an organic light emitting diode (OLED) display,an active-matrix organic light-emitting diode display (AMOLED), a QOLED,a QLED, some other display, or some combination thereof.

The multifocal block 260 adjusts an orientation from light emitted fromthe electronic display 255 such that it appears at particular focaldistances from the user. The multifocal block 260 includes one or morestacked PBP liquid crystal lens structures in optical series, where eachstacked PBP liquid crystal lens structures includes a plurality of PBPliquid crystal lenses and at least one SHWP. Details of liquid crystallenses are discussed in detail below with regard to FIGS. 3A-3C. A SHWPis a half waveplate that reverses a handedness of polarized light inaccordance with a switching state (i.e., active or non-active).Different embodiments, of stacked PBP liquid crystal lens structures arediscussed in detail below with regard to FIGS. 4-7B.

A plurality of PBP liquid crystal lens and at least one SHWP within themultifocal block 260 are stacked in optical series to create a stackedPBP liquid crystal lens structure. A stacked LC structure includes aplurality of PBP liquid crystal lens that are coupled together in amanner that the overall optical power of the stacked LC structure istunable over a range of optical powers. The PBP liquid crystal lenses ina stacked PBP liquid crystal lens structure may be active, passive, orsome combination thereof. Tuning to a particular optical power isaccomplished by controlling the handedness of polarized light as itmoves through the stacked PBP liquid crystal lens structure, appliedvoltage (e.g., in the context of active PBP liquid crystal lenses), andcontrolling a switching state of one or more SHWPs. In some embodiments,each PBP liquid crystal lens within a stacked PBP liquid crystal lensstructure is the same. In other embodiments, one or more of the PBPliquid crystal lenses within a stacked PBP liquid crystal lens structureis different than another PBO liquid crystal lens within the stacked PBPliquid crystal lens structure. For example, one PBP liquid crystal lensprovided ±0.25 diopters of optical power while another LC lens provides±1.0 diopters of optical power.

Moreover, as the individual LC lenses each contribute a relatively lowamount of optical power to the multifocal block 260, each of them mayhave a fast switching time. Accordingly, a stacked PBP liquid crystallens structure may be designed to have a relatively high optical power(e.g., 2 or more diopters) while having a fast switching speed (e.g.,˜300 ms). Accordingly, a stacked PBP liquid crystal structure may beused to provide increased optical power to the multifocal block 260.

Additionally, in some embodiments, the multifocal block 260 magnifiesreceived light, corrects optical errors associated with the image light,and presents the corrected image light is presented to a user of the HMD200. The multifocal block 260 may additionally include one or moreoptical elements in optical series. An optical element may be anaperture, a Fresnel lens, a convex lens, a concave lens, a filter, orany other suitable optical element that affects the blurred image light.Moreover, the multifocal block 260 may include combinations of differentoptical elements. In some embodiments, one or more of the opticalelements in the multifocal block 260 may have one or more coatings, suchas anti-reflective coatings.

FIG. 3A is an example PBP liquid crystal lens 300, according to anembodiment. The PBP liquid crystal lens 300 creates a respective lensprofile via an in-plane orientation (θ, azimuth angle) of a liquidcrystal molecule, in which the phase difference T=2θ. In contrast, aconventional liquid crystal lens creates a lens profile via abirefringence (Δn) and layer thickness (d) of liquid crystals, and anumber (#) of Fresnel zones (if it is Fresnel lens design), in which thephase difference T=Δnd*#*2π/λ. Accordingly, in some embodiments, a PBPliquid crystal lens 300 may have a large aperture size and can be madewith a very thin liquid crystal layer, which allows fast switching speedto turn the lens power on/off.

Design specifications for HMDs used for VR, AR, or MR applicationstypically requires a large range of optical power to adapt for human eyevergence-accommodation (e.g., ˜±2 Diopters or more), fast switchingspeeds (e.g., ˜300 ms), and a good quality image. Note conventionalliquid crystal lenses are not well suited to these applications as, aconventional liquid crystal lens generally would require the liquidcrystal to have a relatively high index of refraction or be relativelythick (which reduces switching speeds). In contrast, a PBP liquidcrystal lens is able to meet design specs using a liquid crystal havinga relatively low index of refraction, is thin (e.g., a single liquidcrystal layer can be ˜2 μm), and has high switching speeds (e.g., 300ms).

FIG. 3B is an example of liquid crystal orientations 310 in the PBPliquid crystal lens 300 of FIG. 3A, according to an embodiment. In thePBP liquid crystal lens 300, an azimuth angle (θ) of a liquid crystalmolecule is continuously changed from a center 320 of the liquid crystallens 300 to an edge 330 of the PBP liquid crystal lens 300, with avaried pitch A. Pitch is defined in a way that the azimuth angle of LCis rotated 180° from the initial state.

FIG. 3C is a section of liquid crystal orientations 340 taken along a yaxis in the PBP liquid crystal lens 300 of FIG. 3A, according to anembodiment. It is apparent from the liquid crystal orientation 340 thata rate of pitch variation is a function of distance from the lens center320. The rate of pitch variation increases with distance from the lenscenter. For example, pitch at the lens center (Λ₀), is the slowest andpitch at the edge 320 (Λ_(r)) is the highest, i.e., Λ₀>Λ₁> . . . >Λ_(r).In the x-y plane, to make a PBP liquid crystal lens with lens radius (r)and lens power (+/−f), the azimuth angle needs to meet: 2 θ=r²/f*(π/λ),where λ is the wavelength of light. Along with the z-axis, a dual twistor multiple twisted structure layers offers achromatic performance onefficiency in the PBP liquid crystal lens 300. Along with the z-axis,the non-twisted structure is simpler to fabricate then a twistedstructure, but is optimized for a monochromatic light.

Note that a PBP liquid crystal lens may have a twisted or non-twistedstructure. In some embodiments, a stacked PBP liquid crystal lensstructure may include one or more PBP liquid crystal lenses having atwisted structure, one or more PBP liquid crystal lenses having anon-twisted structure, or some combination thereof.

Example Stacked PBP Liquid Crystal Lens Structures

Below various designs of stacked PBP liquid crystal lens structures arediscussed. It is important to note that these designs are merelyillustrative, and other designs of stacked structures may be generatedusing the principles described herein. For example, the examples belowdiscuss different designs that each provide 16 different focal planesthat are separated by 0.25 diopters of optical power with a totaloptical power adjustment ranging from 0 diopters to 3.75 diopters. Usingthe principles described herein, one skilled in the art may create otherdesigns for stacked PBP liquid crystal lens structures having differentranges of optical power (0 to 10 diopters, −2 to 2 diopters, etc.),different numbers of focal planes (5, 10, 12, etc.), differentseparation between focal planes (0.1 diopters, 0.3 diopters, etc.). Inother embodiments the stacked PBP LC lens structures can include otheroptical elements in optical series.

FIG. 4 is a generic design of a stacked PBP liquid crystal lensstructure 400 that includes a plurality of active PBP liquid crystallens in optical series, according to an embodiment. The stacked PBPliquid crystal lens structure 400 includes a SHWP 410 and activeelements 415, 420, 425, and 430. An active element is an active PBPliquid crystal lens. In additive states, the active elements 415, 420,425, and 430 add R, 3R, 7R, and 15R, respectively, of optical power,where R (step resolution) is any positive number (e.g., 0.1, 0.25, 0.5etc.). Conversely, in a subtractive state, the active elements 415, 420,425, and 430 subtract −R, −3R, −7R, and −15R, respectively, of opticalpower. This general design provides a PBP liquid crystal lens structurewith a range of optical power adjustment of −15R to 15R, in incrementsof R. And in general, when a number of active PBP lenses is N (positiveinteger), the total number of tuning steps in 2^(N)−1. For example, inFIG. 4, there are four active elements, so there are 15 tuning step thatrange from −15R to 15R, in increments of R.

In FIG. 4, the light in 440 may be left handed circularly polarized(LCP) light or right handed circularly polarized (RCP) light. The stateof the SHWP 410 determines the handedness of the light output from theSHWP 410. For example, if the light in 440 is right handed circularlypolarized light and the SHWP 510 is active, the SHWP 510 reverse thepolarization to left handed. Note when not in a neutral state—an activeelement reverses the handedness of circularly polarized light inaddition to focusing/defocusing the light. Hence, LCP light entering theactive element 410 is output as RCP light with a reduction of opticalpower of −R.

Note, that while FIG. 4 shows 4 active Pancharatnam berry phase LC lenswith 1 active switchable halfwave plate, it may be expanded to more orless active elements. For example, in some embodiments, a stacked PBPliquid crystal lens structure may include just three active elements(e.g., the active elements 415, 420, and 425) and the SHWP 410. In thisembodiment, when R=0.5, N=3, the image focus plane can be tuned from−3.5 Diopter to 3.5 Diopter, with a step resolution 0.5 diopter. Anotherembodiment of a stacked PBP liquid crystal lens structure may includejust two active elements (e.g., the active elements 415 and 420) and theSHWP 410. In this embodiment, when R=0.6, N=2, the image focus plane canbe tuned from −1.8 Diopter to 1.8 Diopter, with a step resolution 0.6diopter.

Turning now to a discussion of a design that is developed using amodification of the generic design of FIG. 4, FIG. 5A is a diagram of astacked PBP liquid crystal lens structure 500 that includes a pluralityof active PBP liquid crystal lens in optical series, according to anembodiment. The stacked PBP liquid crystal lens structure 500 includes aSHWP 410 and active elements 415, 420, and 425. This particular stackedPBP liquid crystal lens structure 400 provides multiple focus planesover a ±3.55 Diopters with a 0.5 Diopter resolution. The stacked PBPliquid crystal lens structure 500 is relatively thin as it includes 4optical elements. A thickness 560 of the stacked PBP liquid crystal lensstructure 500 may be, e.g., approximately 600-1200 μm.

Note that this embodiment is based on light in 540 being right handedcircularly polarized light. In alternate embodiments, the light in 540may be left handed circularly polarized light. In this case, the stackedPBP liquid crystal lens structure 500 would operate in substantially thesame way, except that the active state of the SHWP 510 would bereversed.

FIG. 5B is a table 570 showing example optical power adjustments of thestacked PBP liquid crystal lens structure 500 shown in FIG. 5A,according to an embodiment. The table 570 illustrates how differentoptical powers are achieved from 0 to 3.5 diopters. Note one skilled inthe art, using the principles described herein could easily extend thistable to show how different optical powers are achieved from −3.5diopters to 0 (as shown in FIG. 5C). Recall, that active PBP liquidcrystal lenses have three states, an additive state, a subtractivestate, and a neutral state. The active lens element 415 has an additivestate (+0.5 D), a subtractive state (−0.5 D), and a neutral state (0).The active lens element 420 has an additive state (+1.5 D), asubtractive state (−1.5 D), and a neutral state (0). The active lenselement 425 has an additive state (+3.5 D), a subtractive state (−3.5D), and a neutral state (0). In alternate embodiments, one or more ofthe active elements 415-425 may be associated with differentadditive/subtractive states.

A bottom row 580 of the table 570 illustrates the different amounts ofoptical power that that the stacked PBP liquid crystal lens structure500 is able to provide. The multifocal system controls settings of theSHWP 410 and the active elements 415-425 to select a particular mount ofoptical power to add to the system. In this embodiment, there are 16different selections that range from 0 diopters to 3.5 diopters inincrements of 0.5 diopters. Note, omitted from this table (forsimplicity) are 7 additional selections that range from −3.5 diopters to−0.5 diopters, this is instead shown in FIG. 5C.

For example, to get 2 diopters of optical power, the multifocal systemsets the SHWP 410 to an active state, and active element 415 to itsneutral state. The light in 540 is right handed circularly polarizedlight, the active state of the SHWP 410 reversed the polarization toleft handed. As the active element 415 is neutral it does not add powerto the system or affect the handedness of the light's polarization. Theleft handed circularly polarized light is input into the active element420. Because the input light is left handed, the active element 420 actsin a subtractive state and removes 1.5 diopters of optical power. Notethat the active element 420 also reverses the handedness of the lightsuch that it outputs right handed circularly polarized light. The righthanded circularly polarized light is input into the active element 425,and because the input light is right handed, the active element 425 actsin an additive state and adds 3.5 diopters of optical power to thenegative 1.5 diopters, such that light output from the active element425 adds a total of 2 diopters of optical power to the light input 540.

In another example, to get 0.5 diopters of optical power, the multifocalsystem sets the SHWP 410 to a non-active state, and active elements 420,and 425 to their neutral states. The light in 540 is right handedcircularly polarized light, the non-active state of the SHWP 410 allowslight to be transmitted by the SHWP 410 without changing the handedness.Accordingly, light exiting the SHWP 410 is still right handed circularlypolarized light. The right handed circularly polarized light is inputinto the active element 415, and because the input light is righthanded, the active element 415 acts in an additive state and adds 0.5diopters of optical power. The remaining active elements 420 and 425 arein their neutral state and do not affect the optical power. Accordingly,the PBP liquid crystal lens stack 500 outputs light with an increase in0.5 diopters of optical power. It is important to note that byselectively adjusting the optical power of the PBP liquid crystal lensstack 500, the multifocal system is able to select specific focal planesto present images to a user of a HMD. In the embodiments described abovewith regard to FIGS. 5A and 5B, the multifocal system is able to choosefrom 16 different focal planes that are separated by 0.5 diopters ofoptical power.

FIG. 5C is a table showing example optical power adjustments in thenegative range of the stacked active PBP liquid crystal lens 500structure shown in FIG. 5A, according to an embodiment. The table 590illustrates how different optical powers are achieved from 0 to −3.5diopters.

FIG. 6A is a diagram of a stacked PBP liquid crystal lens structure 600that includes a plurality of active PBP liquid crystal lenses and aplurality of SHWPs, according to an embodiment. The stacked PBP liquidcrystal lens structure 600 includes SHWPs 610, 615, and 620, and activeelements 630, 635, and 640. An active element is an active PBP liquidcrystal lens. In this embodiment, the stacked PBP liquid crystal lensstructure 600 is composed of alternating SHWPs and active elements. Thisparticular stacked PBP liquid crystal lens structure 600 providesmultiple focus planes over a ±3.5 Diopters with a 0.5 Diopterresolution. The stacked PBP liquid crystal lens structure 600 includes 6optical elements, and accordingly is thicker than the stacked PBP liquidcrystal lens structure 500. A thickness 660 of the stacked PBP liquidcrystal lens structure 600 may be, e.g., approximately 900 μm to 1800μm.

FIG. 6B is a table 670 showing example optical power adjustments of thestacked PBP liquid crystal lens structure 600 shown in FIG. 6A,according to an embodiment. The table 670 illustrates how differentoptical powers are achieved. The table 670 illustrates how differentoptical powers are achieved from 0 to 3.5 diopters. Note one skilled inthe art, using the principles described herein could easily extend thistable to show how different optical powers are achieved from −3.5diopters to 0 (e.g., show in FIG. 6C). The active lens element 630 hasan additive state (+0.5 D), a subtractive state (−0.5 D), and a neutralstate (0). The active lens element 635 has an additive state (+1.0 D), asubtractive state (−1.0 D), and a neutral state (0). The active lenselement 640 has an additive state (+2.0 D), a subtractive state (−2.0D), and a neutral state (0). In alternate embodiments, one or more ofthe active elements 630-640 may be associated with differentadditive/subtractive states.

A bottom row 680 of the table 670 illustrates the different amounts ofoptical power that that the stacked PBP liquid crystal lens structure600 is able to provide. The multifocal system controls settings of theSHWPs 610, 615, and 620, and the active elements 630-640 to select aparticular mount of optical power to add to the system. In thisembodiment, there are 16 different selections that range from 0 dioptersto 3.5 diopters in increments of 0.5 diopters. Note, omitted from thistable (for simplicity) are 7 additional selections that range from −3.5diopters to −0.5 diopters, these are instead shown in FIG. 6C.

FIG. 6C is a table 690 showing example optical power adjustments in thenegative range of the stacked active Pancharatnam Berry Phase liquidcrystal lens structure 600 shown in FIG. 6A, according to an embodiment.The table 690 illustrates how different optical powers are achieved from0 to −3.5 diopters. For simplicity, the specific state information foreach SHWP is not shown in FIG. 6C. Given the information disclosedherein, one skilled in the art would be able to determine theappropriate state values to obtain a particular amount of optical power.

FIG. 7A is a diagram of a stacked PBP liquid crystal lens structure 700that includes a plurality of passive PBP liquid crystal lenses and aplurality of SHWPs in optical series, according to an embodiment. Thestacked PBP liquid crystal lens structure 700 includes SHWPs 712, 714,716, 718, 720, and 722, and passive elements 728, 730, 732, 734, 736,and 738. A passive element is a passive PBP liquid crystal lens. In thisembodiment, the stacked PBP liquid crystal lens structure 700 iscomposed of alternating SHWPs and passive elements. This particularstacked PBP liquid crystal lens structure 700 provides multiple focusplanes over a ±3.5 Diopters with a 0.5 Diopter resolution. The stackedPBP liquid crystal lens structure 600 includes 12 optical elements, andaccordingly is thicker than the stacked PBP liquid crystal lensstructure 500, and the stacked PBP liquid crystal lens structure 600. Athickness 748 of the stacked PBP liquid crystal lens structure 700 maybe, e.g., approximately 1380 μm to 2700 μm. However, the thickness couldbe thinner with a bigger diopter resolution per tuning step.

FIG. 7B is a table 770 showing example optical power adjustments of thestacked PBP liquid crystal lens structure 700 shown in FIG. 7A,according to an embodiment. The table 770 illustrates how differentoptical powers are achieved. The table 770 illustrates how differentoptical powers are achieved from 0 to 3.5 diopters. Note one skilled inthe art, using the principles described herein could easily extend thistable to show how different optical powers are achieved from −3.5diopters to 0 (as shown in FIG. 7C). The passive lens element 728 has anadditive state (+0.25 D) and a subtractive state (−0.25 D). The passivelens element 730 has an additive state (+0.25 D) and a subtractive state(−0.25 D). The passive lens element 732 has an additive state (+0.5 D)and a subtractive state (−0.5 D). The passive lens element 734 has anadditive state (+0.5 D) and a subtractive state (−0.5 D). The passivelens element 736 has an additive state (+1.0 D) and a subtractive state(−1.0 D). The passive lens element 738 has an additive state (+1.0 D)and a subtractive state (−1.0 D). In alternate embodiments, one or moreof the passive elements 734-738 may be associated with differentadditive/subtractive states.

A bottom row 780 of the table 770 illustrates the different amounts ofoptical power that that the stacked PBP liquid crystal lens structure700 is able to provide. The multifocal system controls settings of theSHWPs 712, 714, 716, 718, 720, and, 722 to select a particular mount ofoptical power to add to the system (note as these are passive elementsthere is no “neutral” state). In this embodiment, there are 8 differentselections that range from 0 diopters to 3.5 diopters in increments of0.5 diopters. Note, omitted from this table (for simplicity) are 7additional selections that range from −3.5 diopters to −0.5 diopters,these are instead included in FIG. 7C.

FIG. 7C is a table 790 showing example optical power adjustments in thenegative range of the stacked passive PBP liquid crystal lens structure700 shown in FIG. 7A, according to an embodiment. The table 790illustrates how different optical powers are achieved from 0 to −3.5diopters. For simplicity, the specific state information for each HWP isnot shown in FIG. 7C. Given the information disclosed herein, oneskilled in the art would be able to determine the appropriate statevalues to obtain a particular amount of optical power.

Not that while the embodiments of the PBP liquid crystal lens structuresdiscussed above with regard to FIGS. 5A-7C, are specific embodiments.One skilled in the art may design a PBP liquid lens structure usingdifferent numbers of optical elements (e.g., active element, passiveelement, and/or SHWP), different amounts of optical power adjustment(e.g., ±3.75 diopters), different steps between (e.g., R=0.25 diopters),or some combination thereof, than those used in FIGS. 5A-7C.

System Overview

FIG. 8 is multifocal system 800 in which a HMD 805 operates. Themultifocal system 800 may be for use as a virtual reality (VR) system,an augmented reality (AR) system, a mixed reality (MR) system, or somecombination thereof. In this example, the multifocal system 800 includesa HMD 805, an imaging device 810, and an input interface 815, which areeach coupled to a console 820. While FIG. 8 shows a single HMD 805, asingle imaging device 810, and a single input interface 815, in otherembodiments, any number of these components may be included in thesystem. For example, there may be multiple HMDs 805 each having anassociated input interface 815 and being monitored by one or moreimaging devices 460, with each HMD 805, input interface 815, and imagingdevices 460 communicating with the console 820. In alternativeconfigurations, different and/or additional components may also beincluded in the multifocal system 800. The HMD 805 may act as a VR, AR,and/or a MR HMD. An MR and/or AR HMD augments views of a physical,real-world environment with computer-generated elements (e.g., images,video, sound, etc.).

The HMD 805 presents content to a user. In some embodiments, the HMD 805is an embodiment of the HMD 200 described above with reference to FIGS.2A and 2B. Example content includes images, video, audio, or somecombination thereof. Audio content may be presented via a separatedevice (e.g., speakers and/or headphones) external to the HMD 805 thatreceives audio information from the HMD 805, the console 820, or both.The HMD 805 includes an electronic display 255 (described above withreference to FIG. 2B), a multifocal block 260 (described above withreference to FIG. 2B), an eye tracking module 825, a vergence processingmodule 830, one or more locators 225, an internal measurement unit (IMU)215, head tracking sensors 835, and a scene rendering module 840.

As noted above with reference to FIG. 2B-7C, the multifocal block 260activates and/or deactivates one or more SHWPs, one or more active PBPliquid crystal lenses, or some combination thereof to adjust a focallength (adjusts optical power) of the multifocal block 260. Themultifocal block 260 adjusts its focal length responsive to instructionsfrom the console 820.

The eye tracking module 825 tracks an eye position and eye movement of auser of the HMD 805. A camera or other optical sensor inside the HMD 805captures image information of a user's eyes, and eye tracking module 825uses the captured information to determine interpupillary distance,interocular distance, a three-dimensional (3D) position of each eyerelative to the HMD 805 (e.g., for distortion adjustment purposes),including a magnitude of torsion and rotation (i.e., roll, pitch, andyaw) and gaze directions for each eye. In one example, infrared light isemitted within the HMD 805 and reflected from each eye. The reflectedlight is received or detected by the camera and analyzed to extract eyerotation from changes in the infrared light reflected by each eye. Manymethods for tracking the eyes of a user can be used by eye trackingmodule 825. Accordingly, the eye tracking module 825 may track up to sixdegrees of freedom of each eye (i.e., 3D position, roll, pitch, and yaw)and at least a subset of the tracked quantities may be combined from twoeyes of a user to estimate a gaze point (i.e., a 3D location or positionin the virtual scene where the user is looking). For example, the eyetracking module 825 integrates information from past measurements,measurements identifying a position of a user's head, and 3D informationdescribing a scene presented by the electronic display 255. Thus,information for the position and orientation of the user's eyes is usedto determine the gaze point in a virtual scene presented by the HMD 805where the user is looking.

The vergence processing module 830 determines a vergence depth of auser's gaze based on the gaze point or an estimated intersection of thegaze lines determined by the eye tracking module 825. Vergence is thesimultaneous movement or rotation of both eyes in opposite directions tomaintain single binocular vision, which is naturally and automaticallyperformed by the human eye. Thus, a location where a user's eyes areverged is where the user is looking and is also typically the locationwhere the user's eyes are focused. For example, the vergence processingmodule 830 triangulates the gaze lines to estimate a distance or depthfrom the user associated with intersection of the gaze lines. The depthassociated with intersection of the gaze lines can then be used as anapproximation for the accommodation distance, which identifies adistance from the user where the user's eyes are directed. Thus, thevergence distance allows determination of a location where the user'seyes should be focused.

The locators 225 are objects located in specific positions on the HMD805 relative to one another and relative to a specific reference pointon the HMD 805. A locator 225 may be a light emitting diode (LED), acorner cube reflector, a reflective marker, a type of light source thatcontrasts with an environment in which the HMD 805 operates, or somecombination thereof. Active locators 225 (i.e., an LED or other type oflight emitting device) may emit light in the visible band (−380 nm to850 nm), in the infrared (IR) band (−850 nm to 1 mm), in the ultravioletband (10 nm to 380 nm), some other portion of the electromagneticspectrum, or some combination thereof.

The locators 225 can be located beneath an outer surface of the HMD 805,which is transparent to the wavelengths of light emitted or reflected bythe locators 225 or is thin enough not to substantially attenuate thewavelengths of light emitted or reflected by the locators 225. Further,the outer surface or other portions of the HMD 805 can be opaque in thevisible band of wavelengths of light. Thus, the locators 225 may emitlight in the IR band while under an outer surface of the HMD 805 that istransparent in the IR band but opaque in the visible band.

The IMU 215 is an electronic device that generates fast calibration databased on measurement signals received from one or more of the headtracking sensors 835, which generate one or more measurement signals inresponse to motion of HMD 805. Examples of the head tracking sensors 835include accelerometers, gyroscopes, magnetometers, other sensorssuitable for detecting motion, correcting error associated with the IMU215, or some combination thereof. The head tracking sensors 835 may belocated external to the IMU 215, internal to the IMU 215, or somecombination thereof.

Based on the measurement signals from the head tracking sensors 835, theIMU 215 generates fast calibration data indicating an estimated positionof the HMD 805 relative to an initial position of the HMD 805. Forexample, the head tracking sensors 835 include multiple accelerometersto measure translational motion (forward/back, up/down, left/right) andmultiple gyroscopes to measure rotational motion (e.g., pitch, yaw, androll). The IMU 215 can, for example, rapidly sample the measurementsignals and calculate the estimated position of the HMD 805 from thesampled data. For example, the IMU 215 integrates measurement signalsreceived from the accelerometers over time to estimate a velocity vectorand integrates the velocity vector over time to determine an estimatedposition of a reference point on the HMD 805. The reference point is apoint that may be used to describe the position of the HMD 805. Whilethe reference point may generally be defined as a point in space, invarious embodiments, a reference point is defined as a point within theHMD 805 (e.g., a center of the IMU 730). Alternatively, the IMU 215provides the sampled measurement signals to the console 820, whichdetermines the fast calibration data.

The IMU 215 can additionally receive one or more calibration parametersfrom the console 820. As further discussed below, the one or morecalibration parameters are used to maintain tracking of the HMD 805.Based on a received calibration parameter, the IMU 215 may adjust one ormore of the IMU parameters (e.g., sample rate). In some embodiments,certain calibration parameters cause the IMU 215 to update an initialposition of the reference point to correspond to a next calibratedposition of the reference point. Updating the initial position of thereference point as the next calibrated position of the reference pointhelps reduce accumulated error associated with determining the estimatedposition. The accumulated error, also referred to as drift error, causesthe estimated position of the reference point to “drift” away from theactual position of the reference point over time.

The scene rendering module 840 receives content for the virtual scenefrom a VR engine 845 and provides the content for display on theelectronic display 255. Additionally, the scene rendering module 840 canadjust the content based on information from the vergence processingmodule 830, the IMU 215, and the head tracking sensors 835. The scenerendering module 840 determines a portion of the content to be displayedon the electronic display 255 based on one or more of the trackingmodule 855, the head tracking sensors 835, or the IMU 215, as describedfurther below.

The imaging device 810 generates slow calibration data in accordancewith calibration parameters received from the console 820. Slowcalibration data includes one or more images showing observed positionsof the locators 225 that are detectable by imaging device 810. Theimaging device 810 may include one or more cameras, one or more videocameras, other devices capable of capturing images including one or morelocators 225, or some combination thereof. Additionally, the imagingdevice 810 may include one or more filters (e.g., for increasing signalto noise ratio). The imaging device 810 is configured to detect lightemitted or reflected from the locators 225 in a field of view of theimaging device 810. In embodiments where the locators 225 includepassive elements (e.g., a retroreflector), the imaging device 810 mayinclude a light source that illuminates some or all of the locators 225,which retro-reflect the light towards the light source in the imagingdevice 810. Slow calibration data is communicated from the imagingdevice 810 to the console 820, and the imaging device 810 receives oneor more calibration parameters from the console 820 to adjust one ormore imaging parameters (e.g., focal length, focus, frame rate, ISO,sensor temperature, shutter speed, aperture, etc.).

The input interface 815 is a device that allows a user to send actionrequests to the console 820. An action request is a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.The input interface 815 may include one or more input devices. Exampleinput devices include a keyboard, a mouse, a game controller, or anyother suitable device for receiving action requests and communicatingthe received action requests to the console 820. An action requestreceived by the input interface 815 is communicated to the console 820,which performs an action corresponding to the action request. In someembodiments, the input interface 815 may provide haptic feedback to theuser in accordance with instructions received from the console 820. Forexample, haptic feedback is provided by the input interface 815 when anaction request is received, or the console 820 communicates instructionsto the input interface 815 causing the input interface 815 to generatehaptic feedback when the console 820 performs an action.

The console 820 provides content to the HMD 805 for presentation to theuser in accordance with information received from the imaging device810, the HMD 805, or the input interface 815. In the example shown inFIG. 8, the console 820 includes an application store 850, a trackingmodule 855, and the VR engine 845. Some embodiments of the console 820have different or additional modules than those described in conjunctionwith FIG. 8. Similarly, the functions further described below may bedistributed among components of the console 820 in a different mannerthan is described here.

The application store 850 stores one or more applications for executionby the console 820. An application is a group of instructions, that whenexecuted by a processor, generates content for presentation to the user.Content generated by an application may be in response to inputsreceived from the user via movement of the HMD 805 or the inputinterface 815. Examples of applications include gaming applications,conferencing applications, video playback application, or other suitableapplications.

The tracking module 855 calibrates the multifocal system 800 using oneor more calibration parameters and may adjust one or more calibrationparameters to reduce error in determining position of the HMD 805. Forexample, the tracking module 855 adjusts the focus of the imaging device810 to obtain a more accurate position for observed locators 225 on theHMD 805. Moreover, calibration performed by the tracking module 855 alsoaccounts for information received from the IMU 215. Additionally, iftracking of the HMD 805 is lost (e.g., imaging device 810 loses line ofsight of at least a threshold number of locators 225), the trackingmodule 855 re-calibrates some or all of the multifocal system 800components.

Additionally, the tracking module 855 tracks the movement of the HMD 805using slow calibration information from the imaging device 810 anddetermines positions of a reference point on the HMD 805 using observedlocators from the slow calibration information and a model of the HMD805. The tracking module 855 also determines positions of the referencepoint on the HMD 805 using position information from the fastcalibration information from the IMU 215 on the HMD 805. Additionally,the tracking module 855 may use portions of the fast calibrationinformation, the slow calibration information, or some combinationthereof, to predict a future location of the HMD 805, which is providedto the VR engine 845.

The VR engine 845 executes applications within the multifocal system 800and receives position information, acceleration information, velocityinformation, predicted future positions, or some combination thereof forthe HMD 805 from the tracking module 855. Based on the receivedinformation, the VR engine 845 determines content to provide to the HMD805 for presentation to the user, such as a virtual scene, one or morevirtual objects to overlay onto a real world scene, etc.

In some embodiments, the VR engine 845 maintains focal capabilityinformation of the multifocal block 260. Focal capability information isinformation that describes what focal distances are available to themultifocal block 260. Focal capability information may include, e.g., arange of focus the multifocal block 260 is able to accommodate (e.g., 0to 4 diopters), a resolution of focus (e.g., 0.25 diopters), a number offocal planes, combinations of settings for SHWPs (e.g., active ornon-active) that map to particular focal planes, combinations ofsettings for SHWPS and active PBP liquid crystal lenses that map toparticular focal planes, or some combination thereof.

The VR engine 845 generates instructions for the multifocal block 260,the instructions causing the multifocal block 260 to adjust its focaldistance to a particular location. The VR engine 845 generates theinstructions based on focal capability information and, e.g. informationfrom the vergence processing module 830, the IMU 215, and the headtracking sensors 835. The VR engine 845 uses the information from thevergence processing module 830, the IMU 215, and the head trackingsensors 835, or some combination thereof, to select an ideal focal planeto present content to the user. The VR engine 845 then uses the focalcapability information to select a focal plane that is closest to theideal focal plane. The VR engine 845 uses the focal information todetermine settings for one or SHWPs, one or more active PBP liquidcrystal lenses, or some combination thereof, within the multifocal block260 that are associated with the selected focal plane. The VR engine 845generates instructions based on the determined settings, and providesthe instructions to the multifocal block 260.

Additionally, the VR engine 845 performs an action within an applicationexecuting on the console 820 in response to an action request receivedfrom the input interface 815 and provides feedback to the user that theaction was performed. The provided feedback may be visual or audiblefeedback via the HMD 805 or haptic feedback via VR input interface 815.

FIG. 9 is a process 900 for mitigating vergence-accommodation conflictby adjusting the focal length of an HMD 805, according to an embodiment.The process 900 may be performed by the multifocal system 800 in someembodiments. Alternatively, other components may perform some or all ofthe steps of the process 900. For example, in some embodiments, a HMD805 and/or a console (e.g., console 820) may perform some of the stepsof the process 900. Additionally, the process 900 may include differentor additional steps than those described in conjunction with FIG. 9 insome embodiments or perform steps in different orders than the orderdescribed in conjunction with FIG. 9.

As discussed above, a multifocal system 900 may dynamically vary itsfocus to bring images presented to a user wearing the HMD 200 intofocus, which keeps the user's eyes in a zone of comfort as vergence andaccommodation change. Additionally, eye tracking in combination with thevariable focus of the multifocal system allows blurring to be introducedas depth cues in images presented by the HMD 200.

The multifocal system 900 determines 810 a position, an orientation,and/or a movement of HMD 805. The position is determined by acombination of the locators 225, the IMU 215, the head tracking sensors835, the imagining device 810, and the tracking module 855, as describedabove in conjunction with FIG. 8.

The multifocal system 800 determines 920 a portion of a virtual scenebased on the determined position and orientation of the HMD 805. Themultifocal system maps a virtual scene presented by the HMD 805 tovarious positions and orientations of the HMD 805. Thus, a portion ofthe virtual scene currently viewed by the user is determined based onthe position, orientation, and movement of the HMD 805.

The multifocal system 800 displays 930 the determined portion of thevirtual scene being on an electronic display (e.g., the electronicdisplay 255) of the HMD 805. In some embodiments, the portion isdisplayed with a distortion correction to correct for optical error thatmay be caused by the image light passing through the multifocal block260. Further, the multifocal block 260 has activated/deactivated one ormore SHWPS, active PBP liquid crystal lenses, or some combinationthereof, to provide focus and accommodation to the location in theportion of the virtual scene where the user's eyes are verged.

The multifocal system 800 determines 940 an eye position for each eye ofthe user using an eye tracking system. The multifocal system 800determines a location or an object within the determined portion atwhich the user is looking to adjust focus for that location or objectaccordingly. To determine the location or object within the determinedportion of the virtual scene at which the user is looking, the HMD 805tracks the position and location of the user's eyes using imageinformation from an eye tracking system (e.g., eye tracking module 825).For example, the HMD 805 tracks at least a subset of a 3D position,roll, pitch, and yaw of each eye and uses these quantities to estimate a3D gaze point of each eye.

The multifocal system 800 determines 950 a vergence depth based on anestimated intersection of gaze lines. For example, FIG. 10 shows a crosssection of an embodiment of the HMD 805 that includes camera 1002 fortracking a position of each eye 265, the electronic display 255, and themultifocal block 260 that includes stacked PBP liquid crystalstructures, as described with respect to, e.g., FIGS. 2B-7C. In thisexample, the camera 1002 captures images of the user's eyes looking atan image object 1008 and the eye tracking module 825 determines anoutput for each eye 265 and gaze lines 1006 corresponding to the gazepoint or location where the user is looking based on the capturedimages. Accordingly, vergence depth (d_(v)) of the image object 1008(also the user's gaze point) is determined 950 based on an estimatedintersection of the gaze lines 1006. As shown in FIG. 910, the gazelines 1006 converge or intersect at distance where the image object 1008is located. In some embodiments, information from past eye positions,information describing a position of the user's head, and informationdescribing a scene presented to the user may also be used to estimatethe 3D gaze point of an eye in various embodiments.

Accordingly, referring again to FIG. 9, the multifocal system 800adjusts 960 an optical power of the HMD 805 based on the determinedvergence depth. The multifocal system 800 selects a focal plane closestto the determined vergence depth by controlling one or more SHWPs, oneor more active PBP liquid crystal lenses, or some combination thereof.As described above, the optical power of the multifocal block 260 isadjusted to change a focal distance of the HMD 805 to provideaccommodation for the determined vergence depth corresponding to whereor what in the displayed portion of the virtual scene the user islooking.

Additional Configuration Information

The foregoing description of the embodiments of the disclosure have beenpresented for the purpose of illustration; it is not intended to beexhaustive or to limit the disclosure to the precise forms disclosed.Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the abovedisclosure.

Some portions of this description describe the embodiments of thedisclosure in terms of algorithms and symbolic representations ofoperations on information. These algorithmic descriptions andrepresentations are commonly used by those skilled in the dataprocessing arts to convey the substance of their work effectively toothers skilled in the art. These operations, while describedfunctionally, computationally, or logically, are understood to beimplemented by computer programs or equivalent electrical circuits,microcode, or the like. Furthermore, it has also proven convenient attimes, to refer to these arrangements of operations as modules, withoutloss of generality. The described operations and their associatedmodules may be embodied in software, firmware, hardware, or anycombinations thereof.

Any of the steps, operations, or processes described herein may beperformed or implemented with one or more hardware or software modules,alone or in combination with other devices. In one embodiment, asoftware module is implemented with a computer program productcomprising a computer-readable medium containing computer program code,which can be executed by a computer processor for performing any or allof the steps, operations, or processes described.

Embodiments of the disclosure may also relate to an apparatus forperforming the operations herein. This apparatus may be speciallyconstructed for the required purposes, and/or it may comprise ageneral-purpose computing device selectively activated or reconfiguredby a computer program stored in the computer. Such a computer programmay be stored in a non-transitory, tangible computer readable storagemedium, or any type of media suitable for storing electronicinstructions, which may be coupled to a computer system bus.Furthermore, any computing systems referred to in the specification mayinclude a single processor or may be architectures employing multipleprocessor designs for increased computing capability.

Embodiments of the disclosure may also relate to a product that isproduced by a computing process described herein. Such a product maycomprise information resulting from a computing process, where theinformation is stored on a non-transitory, tangible computer readablestorage medium and may include any embodiment of a computer programproduct or other data combination described herein.

Finally, the language used in the specification has been principallyselected for readability and instructional purposes, and it may not havebeen selected to delineate or circumscribe the inventive subject matter.It is therefore intended that the scope of the disclosure be limited notby this detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thedisclosure, which is set forth in the following claims.

What is claimed is:
 1. A varifocal block, comprising: a switchable halfwaveplate (SHWP) that outputs circularly polarized light, and ahandedness of the circularly polarized light is controlled by the SHWPbeing in an active state or a non-active state; a plurality of liquidcrystal (LC) lenses and each LC lens of the plurality of LC lenses isarranged in optical series with each other and the SHWP and each LC lensof the plurality of LC lenses has a plurality of optical states, theplurality of optical states including an additive state that addsoptical power to the LC lens and a subtractive state that removesoptical power from the LC lens; and wherein the handedness of thecircularly polarized light and the plurality of optical states of eachof the plurality of the LC lenses together provide a range of adjustmentof optical power for the varifocal block.
 2. The varifocal block ofclaim 1, wherein each LC lens of the plurality of LC lenses also has aneutral state that does affect optical power, and the range ofadjustment of optical power for the varifocal block is a set of discretevalues of optical power.
 3. The varifocal block of claim 2, whereincircularly polarized light output from the SHWP is received by theplurality of LC lenses.
 4. The varifocal block of claim 2, furthercomprising a plurality of SHWPs that is in optical series with theplurality of LC lenses, and each LC lens of the plurality of LC lensesis directly adjacent to at least one SHWP of the plurality of SHWPs, andthe plurality of SHWPs includes the SHWP.
 5. The varifocal block ofclaim 1, further comprising a plurality of SHWPs that is in opticalseries with the plurality of LC lenses, and each LC lens of theplurality of LC lenses is directly adjacent to at least one SHWP of theplurality of SHWPs, and the plurality of SHWPs includes the SHWP.
 6. Thevarifocal block of claim 5, wherein the range of adjustment of opticalpower for the varifocal block is a set of discrete values of opticalpower, and a size of the range of adjustment scales with a number of LClenses that makes up the plurality of LC lenses.
 7. The varifocal blockof claim 1, further comprising at least one circular polarizer inoptical series with the SHWP, and configured to transmit circularlypolarized light to the SHWP.
 8. The varifocal block of claim 1, whereinthe plurality of LC lenses comprises at least two LC lenses, wherein afirst additive state of a first LC lens differs in optical poweraddition from a second additive state of a second LC lens and a firstsubtractive state of the first LC lens differs in optical powersubtraction from a second subtractive state of the second LC lens. 9.The varifocal block of claim 1, wherein each LC lens of the plurality ofLC lenses is a Pancharatnam Berry Phase (PBP) liquid crystal lens. 10.The varifocal block of claim 1, wherein the varifocal block is acomponent of a head-mounted display.
 11. A head-mounted display (HMD)comprising: a varifocal block that receives content from an electronicdisplay, and presents the content over a plurality of image planes thatare associated with different optical powers of the varifocal block, thevarifocal block comprising: a switchable half waveplate (SHWP) thatoutputs circularly polarized light, and a handedness of the circularlypolarized light is controlled by the SHWP being in an active state or anon-active state, a plurality of liquid crystal (LC) lenses and each LClens of the plurality of LC lenses is arranged in optical series witheach other and the SHWP and each LC lens of the plurality of LC lenseshas a plurality of optical states, the plurality of optical statesincluding an additive state that adds optical power to the LC lens and asubtractive state that removes optical power from the LC lens, andwherein the handedness of the circularly polarized light and theplurality of optical states of each of the plurality of the LC lensestogether provide a range of adjustment of optical power for thevarifocal block, and each value of optical power over the range ofadjustment of optical power corresponds to a different image plane ofthe plurality of image planes.
 12. The HMD of claim 11, wherein each LClens of the plurality of LC lenses also has a neutral state that doesaffect optical power, and the range of adjustment of optical power forthe varifocal block is a set of discrete values of optical power. 13.The HMD of claim 12, wherein circularly polarized light output from theSHWP is received by the plurality of LC lenses.
 14. The HMD of claim 12,further comprising a plurality of SHWPs that is in optical series withthe plurality of LC lenses, and each LC lens of the plurality of LClenses is directly adjacent to at least one SHWP of the plurality ofSHWPs, and the plurality of SHWPs includes the SHWP.
 15. The HMD ofclaim 11, further comprising a plurality of SHWPs that is in opticalseries with the plurality of LC lenses, and each LC lens of theplurality of LC lenses is directly adjacent to at least one SHWP of theplurality of SHWPs, and the plurality of SHWPs includes the SHWP. 16.The HMD of claim 15, wherein the range of adjustment of optical powerfor the varifocal block is a set of discrete values of optical power,and a size of the range of adjustment scales with a number of LC lensesthat makes up the plurality of LC lenses.
 17. The HMD of claim 11,further comprising at least one circular polarizer in optical serieswith the SHWP, and configured to transmit circularly polarized light tothe SHWP.
 18. The HMD of claim 11, wherein the plurality of LC lensescomprises at least two LC lenses, wherein a first additive state of afirst LC lens differs in optical power addition from a second additivestate of a second LC lens and a first subtractive state of the first LClens differs in optical power subtraction from a second subtractivestate of the second LC lens.
 19. The HMD of claim 11, wherein each LClens of the plurality of LC lenses is a Pancharatnam Berry Phase (PBP)liquid crystal lens.